---
sidebar_position: 20
description: What is a flag and how you can create them.
---
import Tabs from '@theme/Tabs';
import TabItem from '@theme/TabItem';


# How to configure a flag

**GO Feature Flag** core feature is to centralize all your feature flags in a source file, and to avoid hosting and maintaining a backend server to manage them.

Your file must be a valid `YAML`, `JSON` or `TOML` file with a list of flags
*(examples: [`YAML`](https://github.com/thomaspoignant/go-feature-flag/tree/main/testdata/flag-config.yaml),
[`JSON`](https://github.com/thomaspoignant/go-feature-flag/tree/main/testdata/flag-config.json),
[`TOML`](https://github.com/thomaspoignant/go-feature-flag/tree/main/testdata/flag-config.toml))*.

:::tip
The easiest way to create your configuration file is to used
[**GO Feature Flag Editor** available at [https://editor.gofeatureflag.org](https://editor.gofeatureflag.org).

If you prefer to do it manually please follow instruction bellow.
:::

## Editor

Creating the first version of the flag is not always pleasant, that's why we have created
[**GO Feature Flag Editor**](https://editor.gofeatureflag.org) a simple editor to create your files.

## Example

A flag configuration looks like:


<Tabs groupId="code">
  <TabItem value="yaml" label="YAML">

```yaml
# This is your configuration for your first flag
first-flag:
  variations: # All possible return value for your feature flag
    A: false
    B: true
  targeting: # If you want to target a subset of your users in particular
    - query: key eq "random-key"
      percentage:
        A: 0
        B: 100
  defaultRule: # When no targeting match we use the defaultRule
    variation: A
  metadata:
    issue_link: https://github.com/thomaspoignant/go-feature-flag/issues/XXX
    description: this is my first feature flag

# A second example of a flag configuration
second-flag:
  variations:
    A: "valueA"
    B: "valueB"
    defaultValue: "a default value"
  targeting:
    - name: rule1
      query: key eq "not-a-key"
      percentage:
        A: 10
        B: 90
  defaultRule:
    name: defaultRule
    variation: defaultValue
  version: "12"
  experimentation:
    start: 2021-03-20T00:00:00.1-05:00
    end: 2021-03-21T00:00:00.1-05:00
```

  </TabItem>
  <TabItem value="json" label="JSON">

```json
{
  "first-flag": {
    "variations": {
      "A": false,
      "B": true
    },
    "targeting": [
      {
        "query": "key eq \"random-key\"",
        "percentage": {
          "A": 0,
          "B": 100
        }
      }
    ],
    "defaultRule": {
      "variation": "A"
    },
    "metadata": {
      "issue_link": "https://github.com/thomaspoignant/go-feature-flag/issues/XXX",
      "description": "this is my first feature flag"
    }
  },

  "second-flag": {
    "variations": {
      "A": "valueA",
      "B": "valueB",
      "defaultValue": "a default value"
    },
    "targeting": [
      {
        "name": "rule1",
        "query": "key eq \"not-a-key\"",
        "percentage": {
          "A": 10,
          "B": 90
        }
      }
    ],
    "defaultRule": {
      "name": "defaultRule",
      "variation": "defaultValue"
    },
    "version": "12",
    "experimentation": {
      "start": "2021-03-20T05:00:00.100Z",
      "end": "2021-03-21T05:00:00.100Z"
    }
  }
}
```

  </TabItem>
  <TabItem value="toml" label="TOML">

```toml
[first-flag.variations]
A = false
B = true

[[first-flag.targeting]]
query = 'key eq "random-key"'

  [first-flag.targeting.percentage]
  A = 0
  B = 100

[first-flag.defaultRule]
variation = "A"

[first-flag.metadata]
issue_link = "https://github.com/thomaspoignant/go-feature-flag/issues/XXX"
description = "this is my first feature flag"

[second-flag]
version = "12"

  [second-flag.variations]
  A = "valueA"
  B = "valueB"
  defaultValue = "a default value"

  [[second-flag.targeting]]
  name = "rule1"
  query = 'key eq "not-a-key"'

    [second-flag.targeting.percentage]
    A = 10
    B = 90

  [second-flag.defaultRule]
  name = "defaultRule"
  variation = "defaultValue"

  [second-flag.experimentation]
  start = 2021-03-20T05:00:00.100Z
  end = 2021-03-21T05:00:00.100Z
```

  </TabItem>
</Tabs>

## Format details

<table>
  <thead>
    <tr>
      <th>Field</th>
      <th>Description</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td width="20%"><strong>flag-key</strong></td>
      <td>Name of your flag.<br/><i>It must be unique.<br/>On the example the flag keys are <code>test-flag</code> and <code>test-flag2</code>.</i></td>
    </tr>
    <tr>
      <td><code>variations</code></td>
      <td>
        <p>
          Variations are all the variations available for this flag.
        </p>
        <p>
          It is represented as a key/value element. The key is the name of the variation and the value could be any types available (<code>string</code>, <code>float</code>, <code>int</code>, <code>map</code>, <code>array</code>, <code>bool</code>).
        </p>
        <p>
          You can have as many variation as needed.
        </p>
        <pre>
          # Some examples<br/>
          variationString: test<br/>
          variationBool: true<br/>
          variationInt: 1000<br/>
          variationFloat: 1000.23<br/>
          variationArray: <br/>  - item1<br/>  - item2<br/>
          variationObj:<br/>  item1: 123<br/>  item2: this is a string<br/>  item3: false<br/>
        </pre>
      </td>
    </tr>
    <tr>
      <td><code>targeting</code><br/><i>(optional)</i></td>
      <td>
        <p>
          Targeting contains the list of rules you have to target a subset of your users.
          <br/>You can have as many target as needed.
        </p>
        <p>This field is an <code>array</code> and contains a list of rules.</p>
        <p><i>See <a href="./rule_format">rules format</a> to have more info on how to write a rule.</i></p>
      </td>
    </tr>
    <tr>
      <td><code>defaultRule</code></td>
      <td>
        <p>DefaultRule is the rule that is applied if the user does not match in any targeting.</p>
        <p><i>See <a href="./rule_format">rules format</a> to have more info on how to write a rule.</i></p>
      </td>
    </tr>
    <tr>
      <td><code>trackEvents</code><br/><i>(optional)</i></td>
      <td>
        <p><code>false</code> if you don't want to export the data in your data exporter.</p>
        <p><b>Default:</b> <code>true</code></p>
      </td>
    </tr>
    <tr>
      <td><code>disable</code><br/><i>(optional)</i></td>
      <td>
        <p><code>true</code> if the flag is disabled.</p>
        <p><b>Default:</b> <code>false</code></p>
      </td>
    </tr>
    <tr>
      <td><code>version</code><br/><i>(optional)</i></td>
      <td>
        <p>The version is the version of your flag.<br/>This string is used to display the information in the notifiers and data collection, you have to update it your self.</p>
        <p><b>Default:</b> <code>""</code></p>
      </td>
    </tr>
    <tr>
      <td><code>metadata</code><br/><i>(optional)</i></td>
      <td>
        <p>This field allows adding a wealth of information about a particular feature flag, such as a configuration URL or the originating Jira issue.</p>
      </td>
    </tr>
    <tr>
      <td><code>scheduledRollout</code><br/><i>(optional)</i></td>
      <td>
        <p>Scheduled allow to patch your flag over time.</p>
        <p>You can add several steps that updates the flag, this is typically used if you want to gradually add more user in your flag.</p>
        <p><i>See <a href="./rollout/scheduled/">Scheduled rollout</a> to have more info on how to use it.</i></p>
      </td>
    </tr>
    <tr>
      <td><code>experimentation</code><br/><i>(optional)</i></td>
      <td>
        <p>Experimentation allow you to configure a start date and an end date for your flag. When the experimentation is not running, the flag will serve the default value.</p>
        <p><i>See <a href="./rollout/experimentation/">Experimentation rollout</a> to have more info on how to use it.</i></p>
      </td>
    </tr>
  </tbody>
</table>




## Advanced configurations

You can have advanced configurations for your flag to have specific behavior for them, such as:
- [Specific rollout strategies](../category/rollout-strategies/)
- [Don't track a flag](../go_module/data_collection/index.md#dont-track-a-flag)
